Project description:siRNA-mediated inhibition compared to untreated cells and cells transfected with nonsense siRNA. Loss of contact inhibition and anchorage-independent growth are hallmarks of cancer cells. In this context, frequent inactivation of the Hippo pathway and subsequent nuclear enrichment of the transcriptional coactivator yes-associated protein (YAP) uncouple cell proliferation and anti-apoptosis from contact inhibition, associated with uncontrolled tumor growth and tumor cell dissemination. However, general molecular mechanisms of tumor-supporting YAP activity remain unclear. In this study, we show that overexpression and nuclear accumulation of YAP in hepatocytes and hepatocellular carcinoma (HCC) cells leads to an induction of the Notch pathways through transcriptional activation of the Notch ligand jagged-1 (Jag-1). This induction of Jag-1 strictly depends on binding of YAP to TEAD4 and does not rely on WNT/β-catenin pathway activity. Co-activation of YAP, TEAD4, Jag-1, and the Notch target gene Hes-1 was significantly higher in HCC from patients with poor prognosis. High-level expression and nuclear accumulation of YAP correlates with Jag-1/Notch activation not only in human HCC tissues, but also in colon and pancreatic cancer tissues. Thus, our data demonstrate that YAP-driven co-activation of the Jag-1/Notch pathway in part facilitates oncogenic properties of the oncogene YAP not only in HCC but also in different gastrointestinal malignancies. Expression profiling of untreated HCC cell lines (control 1), cells transfected with scrambled/nonsense siRNA (control 2), and after siRNA-mediated YAP inhibition.
Project description:siRNA-mediated inhibition compared to untreated cells and cells transfected with nonsense siRNA. Loss of contact inhibition and anchorage-independent growth are hallmarks of cancer cells. In this context, frequent inactivation of the Hippo pathway and subsequent nuclear enrichment of the transcriptional coactivator yes-associated protein (YAP) uncouple cell proliferation and anti-apoptosis from contact inhibition, associated with uncontrolled tumor growth and tumor cell dissemination. However, general molecular mechanisms of tumor-supporting YAP activity remain unclear. In this study, we show that overexpression and nuclear accumulation of YAP in hepatocytes and hepatocellular carcinoma (HCC) cells leads to an induction of the Notch pathways through transcriptional activation of the Notch ligand jagged-1 (Jag-1). This induction of Jag-1 strictly depends on binding of YAP to TEAD4 and does not rely on WNT/β-catenin pathway activity. Co-activation of YAP, TEAD4, Jag-1, and the Notch target gene Hes-1 was significantly higher in HCC from patients with poor prognosis. High-level expression and nuclear accumulation of YAP correlates with Jag-1/Notch activation not only in human HCC tissues, but also in colon and pancreatic cancer tissues. Thus, our data demonstrate that YAP-driven co-activation of the Jag-1/Notch pathway in part facilitates oncogenic properties of the oncogene YAP not only in HCC but also in different gastrointestinal malignancies.
Project description:siRNA-mediated inhibition compared to untreated cells and cells transfected with nonsense siRNA Together with far upstream element binding protein (FBP), the FBP-interacting repressor (FIR) represents a molecular tool for the transcriptional fine tune regulation of target genes. Previous evidence indicates that strong overexpression of FBP in human hepatocellular carcinoma (HCC) supports tumor growth and correlates with poor patient prognosis. However, the role of the transcriptional repressor FIR in hepatocarcinogenesis remains poorly delineated. We show that overexpression of FIR correlates with tumor dedifferentiation and tumor cell proliferation in about 60% of primary HCCs. Elevated FIR levels are associated with genomic gains of the fir gene locus at chromosome 8q24.3 in human HCC specimens. In vitro, nuclear enrichment of FIR supports HCC cell proliferation and migration. Expression profiling of HCC cells after siRNA-mediated silencing of FIR identified the transcription factor DP-1 (TFDP1) as a transcriptional target of FIR. Surprisingly, FIR stimulates the expression of FBP in a TFDP1/E2F-dependent manner. FIR splice variants lacking or containing exon 2 and/or exon 5 are expressed in the majority of HCCs. Specific inhibition of FIR isoforms with and without exon 2 revealed that all FIR splice variants facilitate tumor-supporting effects. This finding was confirmed in xenograft transplantation experiments with lentiviral-infected shRNA targeting all FIR variants as well as FIR with and without exon 2. In summary, high-level nuclear FIR does not facilitate repressor properties but supports tumor growth in HCC cells. Thus, the pharmacological inhibition of FIR might represent a promising therapeutic strategy for HCC patients. Expression profiling of cells transfected with scrambled/nonsense siRNA (control), and after siRNA-mediated FIR inhibition.
Project description:Defective Hippo/YAP signaling in the liver results in tissue overgrowth and development of hepatocellular carcinoma (HCC). Here, we uncover mechanisms of YAP-mediated hepatocyte reprogramming and HCC pathogenesis. We show that YAP functions as a rheostat maintaining metabolic specialization, differentiation and quiescence within the hepatocyte compartment. Importantly, treatment with siRNA-lipid nanoparticles (siRNA-LNPs) targeting YAP restores hepatocyte differentiation and causes pronounced tumor regression in a genetically engineered mouse HCC model (mice with liver-specific Mst1/Mst2 double knockout). Furthermore, YAP targets are enriched in an aggressive human HCC subtype characterized by a proliferative signature and absence of CTNNB1 mutations. Thus, our work reveals Hippo signaling as a key regulator of positional identity of hepatocytes, supports targeting YAP using siRNA-LNPs as a paradigm of differentiation-based therapy, and identifies an HCC subtype potentially responsive to this approach. Mice with liver-specific Mst1/Mst2 double-knockout (Adeno-Cre injected Mst1-/-; Mst2Flox/Flox mice) were monitored for the formation of HCC by ultrasound imaging. Animals were then randomized to be treated by intravenous injection of either siYap-LNPs or siLuciferase-LNPs for a period of 9 days.
Project description:In vertebrates, the evolutionary conserved Hippo pathway fine-tunes organ size under physiological conditions such as tissue regeneration through the transcriptional regulation of pro-proliferative and anti-apoptotic genes. Here we want to identify downstream effectors of YAP, which is the most important transcriptional activator of this pathway.
Project description:The Hippo pathway effectors yes-associated protein (YAP) and WW domain containing transcription regulator 1 (TAZ/WWTR1) support tumor initiation and progression in various cancer entities including hepatocellular carcinoma (HCC). However, to which extent YAP and TAZ contribute to liver tumorigenesis via common and exclusive molecular mechanisms is poorly understood. RNAinterference (RNAi) experiments illustrate that YAP and TAZ individually support HCC cell viability and migration, while for invasion additive effects were observed. Comprehensive expression profiling revealed partly overlapping YAP/TAZ target genes as well as exclusively regulated genes.
Project description:siRNA-mediated inhibition compared to untreated cells and cells transfected with nonsense siRNA Together with far upstream element binding protein (FBP), the FBP-interacting repressor (FIR) represents a molecular tool for the transcriptional fine tune regulation of target genes. Previous evidence indicates that strong overexpression of FBP in human hepatocellular carcinoma (HCC) supports tumor growth and correlates with poor patient prognosis. However, the role of the transcriptional repressor FIR in hepatocarcinogenesis remains poorly delineated. We show that overexpression of FIR correlates with tumor dedifferentiation and tumor cell proliferation in about 60% of primary HCCs. Elevated FIR levels are associated with genomic gains of the fir gene locus at chromosome 8q24.3 in human HCC specimens. In vitro, nuclear enrichment of FIR supports HCC cell proliferation and migration. Expression profiling of HCC cells after siRNA-mediated silencing of FIR identified the transcription factor DP-1 (TFDP1) as a transcriptional target of FIR. Surprisingly, FIR stimulates the expression of FBP in a TFDP1/E2F-dependent manner. FIR splice variants lacking or containing exon 2 and/or exon 5 are expressed in the majority of HCCs. Specific inhibition of FIR isoforms with and without exon 2 revealed that all FIR splice variants facilitate tumor-supporting effects. This finding was confirmed in xenograft transplantation experiments with lentiviral-infected shRNA targeting all FIR variants as well as FIR with and without exon 2. In summary, high-level nuclear FIR does not facilitate repressor properties but supports tumor growth in HCC cells. Thus, the pharmacological inhibition of FIR might represent a promising therapeutic strategy for HCC patients.